In general, a bill processing apparatus, which is one of the embodiments of the paper sheet processing apparatus, is incorporated into a service device such as a game medium rental machine installed in a game hall, a vending machine or a ticket-vending machine installed in a public space, or the like which identifies the validity of a bill inserted from a bill insertion slot by a user and provides various types of products and services in accordance with a value of the bill having been judged as valid. Such a bill processing apparatus comprises a bill conveyance mechanism that conveys a bill inserted into a bill insertion slot, a bill identification part that conducts validity judgment (or also referred to as authenticity judgment) whether the bill to be conveyed is valid or not, and a bill housing part (may also be referred to as a safe) that contains bills having been validated as the bills are stacked sequentially after judging authenticity of the bills.
The bill housing part comprises a placing plate on which bills having been judged as valid are stacked one after another, a presser plate that presses the bills conveyed to and positioned on the placing plate onto a housing position (pressing position), and a driving mechanism that drives the pressing plate to reciprocate toward the placing plate. The bill housing part is configured to be mountable to and demountable from the main body of the bill processing apparatus because it is necessary to replace it with an empty bill housing part when it is filled with the bills stacked on the placing plate.
Such a bill processing apparatus is configured to detect the mounting of the bill housing part (that the bill housing part is mounted accurately at a predetermined position), and to detect a position of the presser plate driven via the driving mechanism as disclosed in Patent Document 1, for example. In detail, at least one movable member which is movable according to the respective movements of the bill housing part and the presser plate is provided, and a movement of the movable member is detected by a plurality of detecting members (optical sensors or the like), whereby the mounting of the bill housing part onto the main body of the bill processing apparatus and a position of the presser plate are detected.    [Patent reference 1] Japanese patent publication No. 3765850.